1. Field of the Invention
The present invention generally relates to seatbelt restraint systems for motor vehicles. More particularly, the present invention relates to a linear pretensioner of a seatbelt restraint system in a motor vehicle.
2. Related Technology
Seatbelt restraint systems used for restraining occupants in motor vehicle seats play an important role in reducing injury to the occupants in the unfortunate event of a vehicle crash. While there are several varieties of seatbelt restraint systems, the conventional “3-point” variety commonly has a lap belt section extending across the pelvis and a shoulder belt section crossing the upper torso of a seated occupant. The lap and shoulder belt sections are each connected to the vehicle structure by anchorages and may be further fastened to each other or formed as portions of a continuous length of seatbelt webbing. Seatbelt restraint systems that are manually secured by the occupant (“active” types) also typically include a latch plate attached to the belt webbing. Such a system further includes a seatbelt buckle attached to the vehicle body structure by another anchorage. The latch plate is received by the buckle thereby allowing the seatbelt restraint system to be fastened, enabling restraint, and unfastened, allowing entrance and exit from the vehicle. Of the anchorages securing the lap and shoulder belt sections, one anchorage typically includes a belt retractor to store the belt webbing. This belt retractor may further act to manage belt tension loads during a crash situation. Seatbelt restraint systems, when deployed, effectively restrain the occupant during a collision.
OEM (Original Equipment Manufacturer) vehicle manufacturers often provide seatbelt restraint systems with pretensioning devices (usually referred to just as a “pretensioner”). These devices induce tension in the seatbelt, either prior to impact of the vehicle during a collision or at an early stage of a sensed impact/collision, so as to enhance occupant restraint performance. This pretensioning takes slack out of the webbing and permits the seatbelt restraint system to engage the occupant earlier in the crash sequence.
One class of pretensioning devices is a pyrotechnic linear pretensioner (PLP). A PLP can be implemented as a pyrotechnic buckle pretensioner (PBP) that is attached to and activated through the seatbelt buckle. In other implementations, the PLP can be attached to a webbing guide loop, either anchorage connected to the opposing ends of the seatbelt webbing or directly to the webbing itself. Since all of the above types of pretensioners linearly pull a seatbelt system component to induce tension in the seatbelt webbing, they are collectively referred to as PLPs.
When a collision occurs, a pyrotechnic charge in the PLP is fired, producing an expanding gas that pressurizes a gas chamber. This pressure forces a piston to move. The piston is connected with the belt system by a cable, a strap or the webbing of the restrain system, and the stroking of the piston tightens or “pretensions” the belt against the occupant. Various examples of PLP and PBP designs are provided in U.S. Pat. Nos. 6,068,664 and 7,823,924, which are hereby incorporated by reference.
Designers of automotive components are constantly striving to reduce the mass of the components as part of the overall goal of providing higher fuel efficiency for motor vehicles. Additionally, these same designers are also constantly striving to reduce costs in automotive components. One way to achieve the above is to reduce packaging or sizing of components.
In accordance with one known design approach, the PLP includes a machined or die cast piston that is coupled to a tubular combustion cylinder. When activated, the piston is sealingly guided along the combustion cylinder. The belt webbing is wound around an actuating profile of the piston such that the length of the belt webbing is shortened by a distance corresponding to twice the distance of the piston stroke. This doubling of the effect of the piston stroke on the belt webbing enables the overall length of the PLP packaging to be shortened. The ability to reduce the width of the packaging would also aid in reducing dimensional sizing of the PLP.